Ingredients:
- 2 oz gin
- 1 oz Yellow Chartreuse
- 3/4 oz fresh lemon juice
- 1/2 oz simple syrup
- Lemon twist, for garnish

Instructions:
1. Add all ingredients to a cocktail shaker filled with ice.
2. Shake vigorously until well chilled.
3. Strain the cocktail into a chilled cocktail glass.
4. Garnish with a lemon twist before serving.

The Chartreuse Sour is a refreshing and herbaceous drink that balances the botanical flavors of gin with the sweet and sour notes of lemon and simple syrup. The addition of Yellow Chartreuse adds a unique and complex flavor profile, making this drink perfect for sipping on a warm summer evening.